1. Field of the Invention
The present invention generally relates to the monitoring and control of data traffic in a telecommunications system.
2. Background Information
Cable-based IP telephony is a simplified and consolidated communication service that can be provided at a lower cost than consumers currently pay to separate Internet, television and telephony service providers. The use of the Internet for real-time voice applications is rapidly increasing. The goal of Internet Protocol (IP) telephony employing cable modem technology is to combine telephony, video, and data signals over a cable distribution infrastructure.
The Voice over IP (VoIP) gateway bridges the public switched telephone network (PSTN) or integrated services digital network (ISDN) with the packet-switched data network (TCP/IP Local Area Network). Such a VoIP gateway is configured to provide IP call control and IP data transport, which includes the compression and decompression of voice channels. VoIP is a relatively new service capable of being supported by Data Over Cable Systems Interface Specification (DOCSIS) cable networks. DOCSIS describes a standard for the cable modem interface between a cable TV operator and a computer. DOCSIS has been accepted as the standard for devices that handle incoming and outgoing data signals across this interface. DOCSIS 1.0 was ratified by the International Telecommunication Union (ITU) in March 1998. Cable modems conforming to DOCSIS are available in many areas where cable operators operate. DOCSIS is an evolving standard which specifies modulation schemes and protocols for exchange of bi-directional signals over cable, allowing version 4 IP traffic to achieve transparent transfer between the Cable Modem Termination System-Network Side Interface (CMTS-NSI) and the Cable Modem to Customer Premise Equipment Interface (CMCI). Upgrades to existing cable modems and DSPs to maximize VoIP quality can be achieved by changing the programming in their EEPROM flash memory.
The DOCSIS 1.1 specification was enhanced with quality of service (QoS) features that are necessary for voice communication and enables the prioritization of packet traffic. This allows cable operators to give certain packets (e.g., voice) the right of way and allows other traffic to be sent with a “best effort” priority as determined by bandwidth availability.
Traditional methods of balancing the processing of voice and non-voice data implement multi-tasking algorithms based on priorities and low-overhead design. These methods have operated successfully under normal conditions. Under stressful or hostile conditions, these methods break down and fail to provide the robustness required for a quality telephony product.
A broadband telephony interface (BTI) can usually support multiple phone calls concurrently with web surfing and file transfer protocol (FTP) operations without any problems. The reported problems arise when the BTI is subjected to both heavy voice traffic and a large volume of data traffic. This traffic can come from the hybrid fiber coaxial (HFC) network, the Ethernet, the universal serial bus (USB), or a home network. It is most likely routed to the same set of interfaces. This traffic can impact voice in the following ways:
(1) It adds to the overall processing load of the processor;
(2) It consumes resources (such as queues and memory buffers) that are needed to support voice;
(3) It consumes transmission opportunities that could have been used by voice;
(4) It may block voice processing at critical sections by holding semaphores;
(5) It may add jitter and delay to voice processing timing when the interface hardware interrupts; and
(6) It may add jitter and delay to voice processing timing where data is processed by the same task. A common failure is when the BTI receives Ethernet traffic at a rate exceeding the data processing capability of the BTI.
Callers using a VoIP gateway send and receive voice packets to and from other VoIP gateways. These packets must be given priority over data packets to ensure that the callers experience smooth, uninterrupted conversations.